#3F7F8C

CSS

:root {
  --mysterious-blue: #3f7f8c;
  --mysterious-blue-rgb: 63 127 140;
  --mysterious-blue-oklch: oklch(0.559 0.068 212.6);
}

.element {
  color: var(--mysterious-blue);
  background-color: hsl(190 38% 40%);
  border-color: oklch(0.559 0.068 212.6);
}

Tailwind CSS v4

@theme {
  --color-mysterious-blue: #3f7f8c;
  --color-mysterious-blue-50: #e0fbff;
  --color-mysterious-blue-100: #cfeef6;
  --color-mysterious-blue-200: #b4dce6;
  --color-mysterious-blue-300: #8fc1cd;
  --color-mysterious-blue-400: #6da9b6;
  --color-mysterious-blue-500: #4a92a1;
  --color-mysterious-blue-600: #407c88;
  --color-mysterious-blue-700: #33636d;
  --color-mysterious-blue-800: #234950;
  --color-mysterious-blue-900: #173337;
  --color-mysterious-blue-950: #081e22;
}

SCSS

$mysterious-blue: #3f7f8c;
$mysterious-blue-rgb: 63, 127, 140;
$mysterious-blue-light: mix(#fff, $mysterious-blue, 20%);
$mysterious-blue-dark: mix(#000, $mysterious-blue, 20%);

.element {
  color: $mysterious-blue;
  box-shadow: 0 0 0 2px rgba($mysterious-blue, 0.35);
}